As an individual ages, the eye is less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia. Similarly, for persons who have had their natural lens removed and an intraocular lens inserted as a replacement, the ability to accommodate is totally absent.
Among the methods used to correct for the eye's failure to accommodate are lenses that have more than one optical power. In particular, contact and intraocular lenses have been developed in which zones of distance and near power are provided. These lenses are disadvantageous because they are difficult to manufacture. Additionally, the use of both distance and near power results in some loss of image contrast at each distance producing a less than completely clear image.
Another known method is to use diffractive simultaneous vision bifocal lenses which incorporate both diffractive optical elements and refractive elements. These lenses are disadvantageous in that light is lost to higher order diffraction. Additionally, the remaining light is split between distance and near vision resulting in less than clear images. Further, these lenses are extremely difficult to manufacture.
Yet another known method is to use birefringent material or a material with wo refractive indices. However, the known birefringent lenses are disadvantageous in use in that the image seen through the lens is not entirely clear.
Therefore, a need exists for a multifocal lens that overcomes some or all of the disadvantages of the prior art lenses.